Vehicle lamp failure warning system having warning circuit completed when lamp is off

ABSTRACT

A lamp failure warning system for a road vehicle has a first lamp circuit which is completed when the lamp is to be illuminated and a second lamp circuit which is completed when the lamp is extinguished but has a resistance sufficiently high to ensure that the lamp is not illuminated. Means is provided sensitive to failure of the lamp when either circuit is completed for giving a warning when the lamp fails.

United States Patent Inventor Allan Bennett Solihull, England Appi. No.833,404 Filed June 16, 1969 Patented Dec. 28, 1971 Assignee Joseph LucasIndustries Limited Birmingham, England Priority July 1, 1968 GreatBritain 31,263/68 VEHICLE LAMP FAILURE WARNING SYSTEM HAVING WARNINGCIRCUIT COMPLETED WHEN LAMP IS OFF 2 Claims, 3 Drawing Figs.

US. Cl 340/85, 340/251 Int. Cl 60% 21/00, B60q 1/02 Field 0! Search340/85, 251

[56] References Cited UNITED STATES PATENTS 3,076,123 1/1963 McDermott340/251 X 3,271,736 9/1966 Brown 340/251 X 3,408,625 10/1968 Skinner340/251 X 3,421,157 1/1969 Atkins 340/251 3,428,943 2/1969 Carp et al.340/251 3,252,157 5/1966 Pabst 340/25] X Primary Examiner-Harold I.Pitts Attorney-Holman & Stern ABSTRACT: A lamp failure warning systemfor a road vehicle has a first lamp circuit which is completed when thelamp is to be illuminated and a second lamp circuit which is completedwhen the lamp is extinguished but has a resistance sufficiently high toensure that the lamp is not illuminated. Means is provided sensitive tofailure of the lamp when either circuit is completed for giving awarning when the lamp fails.

PATENTED 05:28 l97| 3631. 393

sum 2 or 2 INVENTOE BY) "1 m ATT was VEHICLE LAMP FAILURE WARNING SYSTEMHAVING WARNING CIRCUIT COMPLETED WHEN LAMP IS OFF This invention relatesto lamp failure warning systems.

A lamp failure warning system according to the invention comprises afirst lamp circuit which is completed when the lamp is to beilluminated, a second lamp circuit which is completed when the lamp isextinguished and which has a resistance sufficiently high to ensure thatthe lamp is not illuminated, and means sensitive to failure of the lampwhen either the first or the second lamp circuits is completed forgiving a warning when the lamp fails.

In the accompanying drawings, FIGS. I and 2 are circuit diagramsillustrating two examples of the invention, as applied to the electricalsystem of a road vehicle, and FIG. 3 is a circuit diagram showing amodification of FIG. 1.

Referring to FIG. I, the battery 12 of the vehicle has its negativeterminal connected to an earthed supply line 14, and its positiveterminal connected to a supply line 13 through parallel paths one ofwhich contains the ignition switch II of the vehicle and a resistor 5 inseries, and the other of which contains a lighting switch 15. The switch15 when operated operates simultaneously a second switch 16 controllingthe supply of power to a supply line 24, and connected in parallelbetween the lines 24, I4 are four circuits each containing a diode 6 anda lamp 7 in series. The lamps 7 could, for example, be the side andtaillights of the vehicle.

The junction of the diodes 6 and lamps 7 are connected through resistors8 to the bases of four PNP-transistors 9 the emitters of which areconnected to the line 13 and the collectors of which are connectedthrough four resistors 10 to the bases of four NPN transistors 17. Thetransistors 17 have their emitters connected to the line 14, and theircollectors connected through four resistors 18 to the junction of theswitch 11 and resistor 5. The collectors of the transistors 17 arefurther connected through four diodes 19 to the base of anNPN-transistor 20, the emitter of which is connected to the line 14through a resistor 12, and is also connected to the base of anNPN-transistor 21 having its emitter connected to the line 14. Thecollectors of the transistors 20, 21 are connected through a warninglamp 23 to the junction of the resistor 5 and switch 11.

Assuming that the ignition switch 11 is closed, but the switches l5, 16are open, then a circuit is completed through each of the lamps 7 by wayof the resistors 8 and the base emitter paths of the transistor 9 andthe resistor 5. The resistances of the four circuits are such that thelamps 7 are not illuminated, but the transistors 9 are all conducting,so that the transistors 17 also conduct. When the switches 15 and I6 areclosed, the transistors 9 still conduct, but in this case the currentflowing through the diodes 6 to the lamps 7 is sufficient to illuminatethem. Thus, when the ignition switch II is closed, the transistors 9conduct whether the switches 15 and 16 are open or not, but the lamps 7are only illuminated when the switches 15 and 16 are closed.

As long as all the transistors 17 are conducting, no base current issupplied to the transistor 20, and so the transistors 20 and 21 are bothoff. However, when a lamp 7 fails, whether or not that lamp wasilluminated, then one of the transistors 9 will cease to conduct, and sothe corresponding transistor 17 will also cease to conduct, and currentwill flow through the switch 11, one of the resistors 18, one of thediodes 19, the base-emitter of the transistor 20 and the base-emitter ofthe transistor 21 to turn on both transistors 20, 21 and illuminate thewarning lamp 23 to give the required indication.

FIG. 2 shows an alternative arrangement which is suitable for use with apositive earth system. The battery 41 of the vehicle has its positive,earthed, terminal connected to a supply line 43 and its negativeterminal connected to a supply line 44. One side of the lamp 25 to bemonitored is connected to the line 43, and its other side is connectedto the line 44 through a diode 26 and the switch 27 controlling thelamp, the junction of the lamp 25 and diode 26 being connected through aresistor 28 at the base of an NPN-transistor 29, the emitter of which isconnected to the line 44 through the ignition switch 42 and thecollector of which is connected through a resistor 31 to the line 43.The collector of the transistor 29 is also connected through a diode 32to the base of an NPN- transistor 34 having its emitter connected to thebase of an NPN-transistor 33, the emitter of which is connected to theline 44, through the switch 42. The collectors of the transistors 33 and34 are connected through a warning lamp 35 to the line 43.

In operation, assuming that the switch 37 is open and the ignitionswitch 42 is closed, current flows through the warning lamp 25 and theresistor 28 turns the transistor 29 on, but the current flowingthroughthe lamp 25 is insufficient to illuminate it. When the switch 27 isclosed, the lamp 25 is illuminated, and the transistor 29 is still heldon. Thus, as long as the lamp 25 is operating satisfactorily, thetransistor 29 prevents current from flowing through the diode 32.However, when the lamp fails, whether or not the switch 27 is open, thetransistor 29 is turned off and current flows through the resistor 31and diode 32 to turn on transistors 34 and 33, so that the warning lamp35 is illuminated.

It will be noted that in FIG. I the lamp switch I5, 16 is a doubleswitch, and the resistor 5 is employed, whereas in FIG. 2 a single lampswitch 27 is used and there is no equivalent to the resistor 5. Thereason for this is that in FIG. 1 the low-gain PNP-transistor 9 requirea low valve for resistors 8 in order that insufficient base drive can besupplied to saturate them. In order to prevent excessive powerdissipation with the lighting switch open, the resistor 5 isincorporated to increase the base-emitter resistance of each of thetransistors 9. It is then necessary to use the two-part lighting switchl5, 16 to isolate the line 24 from the line 13 when the switches l5, 16are open. This problem does not arise in FIG. 2, where the transistors29 equivalent to the transistors 9 in FIG. 1 are NPN-transistors whichhave higher gains.

In systems where it is inconvenient to use a double switch 15, I6, themodification shown in FIG. 3 can be used. In FIG. 3, only the circuitassociated with one lamp 7 is shown, and it will be seen that comparedwith FIG. I the part 16 of the switch 15, 16 is omitted, with the diode6 having its anode connected through the switch 15 directly to thepositive battery terminal. The resistor 5 is also omitted, so that theswitch 11 completes a direct connection to the line 13. Each transistor9 is now replaced by a pair of transistors 9a and 9b. The transistor hasits base connected to the resistor 8 and its emitter connected to theline 13, while its collector is connected to the base of the transistor9b, the collector of which is connected to the line 13 and the emitterof which is connected to the resistor 10. The transistors 90 and 9b forman effective high-gain PNP-combination, and using this arrangement theresistor 8 can be chosen so that the circuit operates satisfactorilywithout the necessity of the resistor 5, and the consequent requirementfor a double switch 15, 16.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

I. A lamp failure warning system comprising a first lamp circuit whichis completed when the lamp is to be illuminated, a second lamp circuitwhich is completed when the lamp is extinguished, and which has aresistance sufficiently high to ensure that the lamp is not illuminated,said first lamp circuit when completed increasing the current flow inthe lamp to illuminate the lamp, and a second lamp circuit remainingcompleted when the first lamp circuit is completed, and means operableby said second lamp circuit and sensitive to failure of the lamp wheneither the first or second lamp circuits is completed for giving awarning when the lamp falls.

2. A lamp failure warning system for a road vehicle, comprising a seriescircuit connected across the battery of the vehicle and including alighting switch, a diode and a lamp, a second circuit connected acrossthe vehicle b ttery and including the ignition switch of the vehicle,the emitter-base path of a transistor, a resistor and said lamp, saidsecond circuit being completed when the ignition switch is closed tocause the transistor to conduct but the current flowing through the lampbeing insufi'rcient to energize it until the lighting switch is closed,and means operable by the collector current of said transistor forgiving a warning when the baseemitter current of said transistor isbroken by failure of said lamp. 5

1. A lamp failure warning system comprising a first lamp circuit whichis completed when the lamp is to be illuminated, a second lamp circuitwhich is completed when the lamp is extinguished, and which has aresistance sufficiently high to ensure that the lamp is not illuminated,said first lamp circuit when completed increasing the current flow inthe lamp to illuminate the lamp, and a second lamp circuit remainingcompleted when the first lamp circuit is completed, and means operableby said second lamp circuit and sensitive to failure of the lamp wheneither the first or second lamp circuits is completed for giving awarning when the lamp fails.
 2. A lamp failure warning system for a roadvehicle, comprising a series circuit connected across the battery of thevehicle and including a lighting switch, a diode and a lamp, a secondcircuit connected across the vehicle battery and including the ignitionswitch of the vehicle, the emitter-base path of a transistor, a resistorand said lamp, said second circuit being completed when the ignitionswitch is closed to cause the transistor to conduct but the currentflowing through the lamp being insufficient to energize it until thelighting switch is closed, and means operable by the collector currentof said transistor for giving a warning when the base-emitter current ofsaid transistor is broken by failure of said lamp.